Living Environment Regents Review Practice Reproduction and Development Question 7
Wednesday, 01 July 2009 11:48
Which statement best explains why invertebrates regenerate lost tissue more readily than most vertebrates do?
A)They contain specialized cells that produce the hormones necessary for this process.
B)Cells of invertebrates exhibit a higher degree of uncontrolled cell division than vertebrate cells do.
C)They reproduce asexually, but vertebrate animals reproduce sexually.
D)They have more undifferentiated cells than vertebrate animals have.
Correct Answer: Option D - They have more undifferentiated cells than vertebrate animals have.
Invertebrates, animals without a backbone such as an earthworm, are simpler than vertebrates such as a human. Therefore, their cells are not as complex and they may be able to regenerate or grow lost body parts easier than a more complex animal. Regeneration of parts or, in some cases, nearly the entire body of an organism from a part, is more common than one might think. Many protists like the amoeba that have been cut in half can grow back into a complete organism so long as enough of the nuclear material is undamaged. Severed cell parts, such as flagella, can also be regrown in protists. New plants can be grown from cuttings, and plants can often be regenerated from a mass of fully differentiated cells (such as a section of a carrot root), which, if isolated in a suitable environment, turn into a mass of undifferentiated cells that develop into a fully differentiated organism. The capacity for regeneration varies widely in animals, with some able to regenerate whole limbs and others not, but the capacity is reduced significantly in more complex animals. Certain simple invertebrates like the hydra are always regenerating themselves. If, cut into tiny pieces that are then mixed up, the pieces can reorganize themselves and grow back into a complete organism. Flatworms have the capacity to regenerate themselves from only a small mass of cells. In many animals, these regenerated body parts are not as large as the originals but are usually sufficient to be functional. Many higher animals such as mammals regularly regenerate certain tissues such as hair and skin and portions of others such as bone, but most tissues cannot be regenerated.
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